The effects of floods and sockeye salmon on streambed morphology.

Streambed changes resulting from floods and spawning activity of sockeye salmon were monitored in two gravel bed streams in Stuart-Takla Experimental Watersheds of the Upper Fraser River basin, British Columbia, Canada. The streams have a forced pool-riffle morphology, and are utilized yearly by 7,000 to 10,000 sockeye salmon for spawning. Streambed mapping was performed before and after nival floods, summer floods and sockeye salmon spawning events in 1996 and 1997. Flood transport moves gravel out of pools, increases gravel bar heights, creates scour holes, and establishes a distinct thalweg. Sockeye spawning, which follows the floods, removes gravel from the edges and surface of the bars, and fills in the pools, scour holes and thalweg. The stream morphology is thus altered in opposing fashion by two different processes. It was found that the cut and fill volumes are similar in magnitude but that the two processes affect the stream in a very different manner.